[Bud9051]

Instructions usually call for being opened on both sides. Have they installed the actual ridge vent yet?

I'm sure he will have an excuse but you want to see the mfgs instructions and make him follow them. We can review the required amount of ventilation you should be looking for.

Add your nearest big city to your profile so we will have an idea as to your climate abd building methods.

Bud

 

[Bud9051]

On a roof that has a ridge board as yours does the proper way is to cut the opening one inch to each side of that center board. Here's a link with an illustration.

If he has some reason for the half (A$$) job we need to hear it, but I can't think of any that would follow any ridge mfgs guideline. Basically he has provided half the high NFA (net free area) for the suggested ventilation. Will that be enough?? We can only guess at this point but you are in a cold climate (OH) so venting unwanted moisture is important.

It will be easier for him to drag his feet and hope you go away. If you haven't paid in full you could use that money to motivate his, but removing what is there and re-installing it would be a poor job. The existing vent should be replaced with new and all of the extra holes created should be sealed.

He has provided half the vent capacity of that ridge vent. How much you actually need has not been determined and we can help.

Bud

 

[Bud9051]

Ventilation guidelines are dependent upon the age of the house and how well the ceiling to attic layer has been sealed, usually just normal which does not qualify as sealed. Older homes definitely not unless a major effort was undertaken to do such sealing.

Anyway the normal guidelines are 1 ft² of NFA (net free area) for every 150 ft² of attic floor. That number is then divided in half with half going high and half going low. Soffit vents and ridge vents are a common combination and each vent has a rated NFA.

If the house is newish and was specifically air sealed then you can use half of that number (1 ft² NFA for every 300 ft²). But you would likely be running a heat recovery ventilator in such a tight home.

Ridge vents are usually rated to provide 18 in² of NFA per linear foot, 9 on each side. A 40' ridge vent would provide 720 in² or 5 ft². Give us the size and age of your house and a description and we will factor those details in.

Bud

 

[Bud9051]

As I remember some ridge vents provide a ¾" gap on each side, thus 1.5" total opening to the air. Multiply that times 12" and you get their claimed 18 in² per linear foot (9 on each side).

With an attic floor area of 1360 you would need a total NFA of 9 ft², 4.5 ft² high and 4.5 ft² low. Some back of hand calculations with your 1.25" gap I came up at just over 4 ft² for high area. I hate cutting this guy any slack but from a technical point of view your high vent area will do just fine. Add to that any additional air sealing you do, which is always a top priority, will reduce the suggested NFA. Also, the suggested NFA is not a hard number in that 10% short and you will have a disaster. As long as you have low vents half of what you ended up with would work.

Bud

 

[Bud9051]

Soffit venting is probably the most common and traditional ranch from 1966. However, back then they weren't a generous with how much venting they installed, often a few smaller vents along each overhang. That in turn often gets covered with vented soffit panels without enlarging the openings they covered. You should do some checking to see what you have Baffles on the inside in each rafter bay as well. And as always, pictures.

Bud

 

[Bud9051]

Which "guidelines" are you pulling this from?

There are many sources and the definition changes a bit from author to author. This link touches on both the 1/300 and 1/150 rules but their reason stated isn't exactly complete (IMO).

The need for a vapor barrier has been replaced by good air sealing and many modern homes are addressing that issue at the time of construction. With an existing home retrofitting a good air sealing job is difficult so ventilation area should lean towards the 1/150 guidelines.

Keep in mind that ALL referenced, even codes, pointing at either 1/150 or 1/300 are NOT exact requirements. Anything close counts in ventilation.

Bud

 

[Bud9051]

Unfortunately quoting any code specifying 1/300 or 1/150 would not be exactly what is needed, other than what a building inspector might think is needed. This is a case of a wild guess being passed around until everyone forgot it was a guess from the start so it became the code. Fortunately Bill Rose did some digging and provided us with some history on this ventilation requirement and why we need to consider it as a "general" starting point and not an absolute number. I have read here on the forum where posters have taken these calculations to be a must or failure is certain.

We can review some of the variables but one example is NFA. It is an imperfect number even when we can find it stated by the manufacturer. When not listed somewhere we must guess at a number typical of that style vent. In effect we end up using a guess for calculating an exact number, not good and not something that should result in failing an inspection.

Writing building codes is not easy and building inspectors don't like complex requirements so they get 1/150 or 1/300 as their only choice and despite the vagueness the masses end up following it.

Bud

 

[Bud9051]

@ craig, a different part of the house, siding, but an example of what some contractors will hide. When I removed the old hardboard siding after 30+ years I uncovered to original felt paper used over the plywood. To one side of my front door, standard cape, and between the two windows he had apparently run out of felt. No problem, he just collected all of the scraps and patchwork style covered that 1/4 of the front of the house. Some pieces were 4" by 16" with no attempt to overlap to direct any water down to the bottom. He just wanted it all to look black and quickly covered it all with siding.

When they know they will be long gone before anyone will discover their short cut they may do anything that puts money in their pocket.

Bud